This invention relates to internal combustion engine systems and, more particularly, to improvements in such systems which decrease noxious emissions, increase operating efficiency, and reduce maintenance requirements.
The emission of noxious gases by internal combustion engines (including Brayton turbine combustion cycle systems, diesel engines, Otto-cycle spark ignition engines, and the like) is a continuing problem. From an environmental standpoint, the noxious gases are unacceptable pollutants, and government has become heavily involved in the regulation of emission of such noxious gases. The cost to society is very substantial, as measured by the degradation of the environment plus the cost of limiting or controlling such emissions, which is ultimately paid by the consumer. It is also well known that a combustion process which results in a high level of noxious emissions is generally less efficient, from the standpoint of energy output, than the same process operating in a manner which results in a lower level of noxious emissions.
It has long been recognized in the art that controlled injection of water into a combustion engine can, under certain conditions, increase the operating efficiency and reduce the noxious emissions in the exhaust. One drawback of prior art water injection has been the almost immediate corrosion which can occur when water is introduced (either intentionally or during an injection malfunction) directly to hot engine components.
The products of combustion are rich in oxides of nitrogen (NO.sub.x) formed when unburned oxygen combines with nitrogen, the inert component of ambient air at elevated temperatures. NO.sub.x is an environmental hazard. Excess air is technically defined as that quantity in excess of the theoretical quantity required for complete combustion of a fuel. The combustion turbine, to which the present invention has particular although not exclusive application, operates at very high excess air rates. The high excess air rates produce high levels of noxious and toxic NO.sub.x. Fuel-bound nitrogen and sulfur also cause problems.
It is know that NO.sub.x and other noxious emissions can be reduced by water injection in the combustion chamber, which reduces flame temperatures. Unfortunately, heat needed to vaporize the injected water is wasted energy. Also, to preclude scaling, costly ultra-pure water is needed. Externally produced steam has also been used as an injection medium to reduce NO.sub.x, but this requires substantial additional energy and adds additional environmental hazards due to volatile anticorrosive chemicals found in high pressure steam.
In the U.S. Pat. No. 4,313,300, the quantity of NO.sub.x emissions generated by a combined gas turbine-steam boiler power plant is controlled by recycling steam boiler exhaust gas to the air compressor of the gas turbine, thereby increasing the combustor inlet humidity.
In the U.S. Pat. No. 4,231,333 fuel or water injection into an internal combustion engine is controlled based upon detection of predetermined engine conditions, such as pressure within the engine intake manifold.
In the U.S. Pat. No. 4,417,547 atomized fluid from a nozzle is injected into the carburetor of an internal combustion engine, the rate of fluid injection being varied in response to variations in engine speed and engine load.
It is among the objects of the present invention to provide internal combustion engine systems which improve over the described types of systems, and which decrease noxious emissions, increase operating efficiency, and reduce maintenance requirements.